The development of material science is one of the important factors of national scientific and technological progress. The advantages and disadvantages of the structural materials performance are mainly determined by their mechanical properties, including shock resistance of the materials, fatigue properties and plastic manufacturing capability. In order to develop new type and high performance materials, the deformation mechanism of the materials in nano, atomic or even sub angstrom scale should be understood in depth. Transmission electron microscopy (TEM) is one of the important means to study material microstructure, and by non TEM in-situ study method, some researchers cut out the materials in different deformation stage respectively as samples and observe their microstructure, thus infer the deformation mechanism of the materials; due to the limit that the observation range (in nano scale) and observation area in TEM are not the same area, sometimes the accurate deformation mechanism of the material is hard to be obtained. In recent years, some researchers and equipment manufacturers devote to develop in-situ TEM deformation technology, by applying force field on the samples in the TEM, in-situ observation of microstructure evolution of the same area of the samples is realized, which provides a favorable means to study the elastic and plastic deformation mechanism of the materials.
At present, the drive modes applying stress load to micro and macro samples mainly comprise: electrostatic drive, memory alloy drive, piezoelectric drive, fluid drive, electromagnetic drive and thermal drive et. al. Therein electrostatic drive and fluid drive are not suitable for TEM due to a larger size. The drive force of the electromagnetic drive is less and magnetic and not suitable for TEM. The outputs of force and displacement of memory alloy drive are unstable and also not suitable for TEM. At present commercialized in-situ mechanical sample holders for TEM are mainly driven by the modes of piezoelectric ceramic drive, and typical commercialized products include: 671 and 654 type mechanical sample holders of American GATAN company, PI95 type mechanical sample holder of American Hysitron company et. al. Piezoelectric ceramic with three-dimensional drive and high-precision is placed at the through hole of the sample holder shaft by these commercialized sample holders to realize the stretch and compression of the samples; its advantages are: experimental convenience, no effect from temperature, accurate control of deformation, quantitative test of sample pressure; but the piezoelectric ceramic is located at the back end of the shaft, limiting the function of tilt of the sample holder in the direction of Y axis, so it is difficult to ensure electron beam incidence along the low index crystal face of the sample, and further clear electron diffraction patterns and high resolution images in atomic scale or sub angstrom scale cannot be obtained.
In order to solve the limit that the double-axis tilt of commercialized sample holders cannot be realized, many research groups have developed in-situ mechanical sample holders or drive modes for TEM by which double-axis tilt can be applied. The bimetallic strip driver for TEM was researched and developed by Han Xiaodong et. al from Beijing University of Technology (Patent No.: CN 200910086803), by the principle of thermal expansion drive the function of double-axis tilt is realized while deformed materials are stretched by large strain, thus clear atomic lattice images and high quality diffraction images are obtained. The advantages of this method are in that: (1) The load of surface internal force is realized under the premise of double-axis tilt (X:±30°/±20°, Y:±30°/±20°) ensured; (2) Its stretch velocity can be controlled very well by adjusting temperature controller and the regulation of 10−5-10−1S−1 of strain rate can be realized; (3) large deformational behavior of bimetallic strip can be realized when the temperature is below 100° C., thus large strain stretch experiment on the samples can be carried out. The disadvantage of this method are in that: (1) bimetallic strip tensioner must be driven by temperature control, and the temperature effect is introduced while the deformation mechanism of the material is studied, which brings the difficult to study the deformation mechanism of some temperature sensitive materials; (2) the drive force outputted is less and difficult to drive the samples with large size, high elastic modulus.
Han Xiaodong et. al from Beijing University of Technology developed the in-situ deformation technology for TEM based on V shape beam thermal drive (Patent No.: ZL 2015 2 0191419.X). Its advantages are: the displacement outputted is large, and oversized deformation stretch of the samples can be realized. Its uniaxiality is good, and the shear stress will not be generated in the horizontal direction of the samples. But at the same time, some disadvantages exist, for example: the realization of the drive depends on temperature as well and it is difficult to study the deformation mechanism of some temperature sensitive materials, and due to its higher drive temperature, it is not suitable to be used coordinating with mechanical sensor, which affect the quantitative output of mechanical properties of samples.